One prior art embodiment of a heat exchanger as described in Japanese Patent Application Publication No. 63-112065 is shown in FIGS. 1-3. As shown in the figures, condenser 50 includes a plurality of adjacent, essentially flat tubes 51 having an oval cross-section and open ends which allow refrigerant fluid to flow therethrough. A plurality of corrugated fin units 52 are disposed between adjacent tubes 51. Flat tubes 51 and fin units 52 jointly form heat exchange region 100. Cylindrical header pipes 53 and 54 are disposed perpendicular to flat tubes 51 and may have, for example, a clad construction. The diameter and length of header pipes 53 and 54 are substantially equal to the thickness and height, respectively, of heat exchange region 100. Accordingly, header pipes 53 and 54 protrude only negligibly relative to heat exchange region 100 when the heat exchanger structure is assembled.
As shown in FIG. 3, each of header pipes 53 and 54 includes outer tube 60 and inner tube 61. Outer tube 60 is preferably made of aluminum. Inner tube 61, made of a metal material, is brazed to the inner surface of outer tube 60. Outer tube 60 has a plurality of slots 62 disposed therethrough. Flat tubes 51 are fixedly connected to header pipes 53 and 54 and are disposed in slots 62 so that the open ends of flat tubes 51 communicate with the hollow interiors of header pipes 53 and 54. Inner tube 61 includes a plurality of portions 63 which define openings corresponding to slots 62. Portions 63 are brazed to the ends of flat tubes 51 and ensure that tubes 51 are hermetically sealed within header pipes 53 and 54 when the tubes are inserted in slots 62.
In operation, compressed refrigerant gas from an external compressor coupled to inlet union joint assembly 531 flows through the joint and into the upper cavity of header pipe 53. In header pipe 53, the refrigerant is distributed so that a portion of the gas flows through each of flat tubes 51 which is disposed above the location of partition wall 532, and into an upper portion of the upper cavity of header pipe 54. Thereafter, the refrigerant in the upper portion of the upper cavity of header pipe 54 flows downwardly into a lower portion of the upper cavity of header pipe 54. The refrigerant is distributed therein so that a portion of the refrigerant flows through each of flat tubes 51 disposed below the location of partition wall 532 and above the location of partition wall 542, and into an upper portion of the lower cavity of header pipe 53. The refrigerant in the upper portion of the lower cavity of header pipe 53 then flows downwardly into a lower portion of the lower cavity. At this point, the refrigerant is again distributed so that a portion of the refrigerant flows through each of flat tubes 51 disposed below the location of partition wall 542, and into the lower cavity of header pipe 54. As the refrigerant gas sequentially flows through flat tubes 51, heat from the refrigerant gas is exchanged with the atmospheric air flowing through corrugated fin units 52. The condensed liquid refrigerant in the lower cavity of header pipe 54 flows out of the cavity through outlet union joint assembly 541 and into an external receiver coupled to the joint assembly.
Another prior art embodiment of a heat exchanger as described in U.S. Pat. No. 4,615,385 is shown in FIG. 4. Each header pipe 53 and 54 has a plurality of slots 62 along one of its surfaces for receiving open ends of flat tubes 51. The surface portions of the header pipe between the slots 62 are shaped as outwardly extending convex domes 70 as shown in the FIG. 4.
In both of the above embodiments, open ends of flat tubes 51 extend considerably into the interiors of header pipes 53 and 54. Since the refrigerant introduced through inlet union joint assembly 531 flows in the longitudinal direction of header pipes 53 and 54, (i.e., perpendicular to flat tubes 51) the flow direction of the refrigerant has to turn suddenly to the open ends of flat tubes 51 to travel therethrough.
Accordingly, vortexes as shown by arrows A occur adjacent to the open ends of flat tubes 51. As a result, the pressure loss of the condenser is increased. In addition, according to the occurrence of vortexes, the flow speed of the refrigerant is reduced thereby necessitating the use of an excess volume of the refrigerant in the condenser.